1. Field of the Invention
The present invention relates to a method for synthesizing benzotriazole in a one-pot reaction that does not require isolation of intermediates or a precious metal catalyst.
2. Description of the Prior Arts
Benzotriazole is frequently used in cosmetics and sunscreens or the like to absorb ultraviolet (UV) light and prevent harmful effects of UV light.
Benzotriazole absorbs UV, especially at wavelengths of 280 nm and 320 nm in the UV-B range and 320 nm and 400 nm of the UV-A range. Therefore, simple and efficient synthesis routes of benzotriazole are much desired. Prior patents U.S. Pat. Nos. 3,715,334, 3,947,436, 4,051,161, 4,122,233, 4,188,451, 4,233,430, 4,316,033, 4,342,742, 4,373,060, 4,457,911, 4,489,057, 4,490,356, 4,696,969, 4,814,162, 4,851,587, 4,859,759, 4,868,251, 5,089,250, EP 0,138,321, EP 0,354,145 and GB 2,077,280 disclosed several methods for preparing benzotriazole. These methods use 2-(2-hydroxy-5-methylphenyl) benzotriazole or its derivatives as a reactant to react with chloroalkyl propylene in a basic organic solvent at high temperature through a Claisen rearrangement. However, the Claisen rearrangement creates many by-products. Therefore, these methods must include a separation step to remove a desired benzotriazole product and therefore has the following drawbacks:
1. Polar organic solvents that easily bring water are used in the reaction. However, water proceeds through a different reaction path and competes with the desired reaction raising an amount of undesired by-products. Therefore, the separation step is further complicated and slowed.
2. Low reaction yields.
3. A rate of reaction is higher between 180° C. and 250° C.
4. After forming an initial intermediate, these methods require a separation step to separate by-products from the intermediate before proceeding to a Claisen rearrangement, therefore, requiring multiple steps and reaction vessels.
5. Purification requires large amounts of organic solvents that require expensive disposal and pollute the environment.
6. These methods require a metal catalyst, frequently particles of a metal catalyst that require a large investment for procurement. The metal catalyst is not easily separated from the solvent, and any that remains causes greater environmental damage if released and directly increases costs of the benzotriazole. The present invention has arisen to provide a method for synthesizing benzotriazole to overcome and obviate the drawbacks of the conventional methods.